Natural gas has several advantages over other hydrocarbon fuels that are combusted in internal combustion engines. For example, natural gas is less expensive relative to other hydrocarbon fuels. Moreover, for example, natural gas burns cleaner during operation of the internal combustion engine relative to other hydrocarbon fuels. By burning cleaner, a reduced amount of combustion byproducts such as carbon monoxide, oxides of nitrogen or hydrocarbons are released into the environment during operation of the internal combustion engine. In addition, because lubricants of the internal combustion engine become contaminated with the combustion byproducts over a time period, the production of a reduced amount of combustion byproducts results in less contamination of the lubricants over the time period thereby increasing the useful life of the lubricants.
One type of internal combustion engine is a diesel engine. Diesel engines combust fuel by compressing a mixture of air and fuel to a point where the fuel is ignited by heat which results from such compression. When natural gas is used as a fuel in a diesel engine, the natural gas does not readily ignite as it is compressed. In order to overcome this problem, an ignition source is provided to ignite the natural gas. The ignition source may be provided by a spark plug similar to those used in spark ignition engines. However, in certain types of diesel engines (e.g. dual fuel engines), the ignition source is provided by injecting a small amount of diesel fuel with a pilot fuel injector into the mixture of air and natural gas. As the mixture of air, natural gas, and diesel fuel is compressed, the diesel fuel ignites, which in turn ignites the natural gas.
In larger types of diesel engines, it is common to lubricate the intake valves of the combustion chambers. Such lubrication increases the life of the diesel engine. In this regard, a typical lubricating system would include an oil injector positioned to advance a small quantity of lubricating oil into an intake manifold of the diesel engine. During an intake stroke of the engine, the lubricating oil is advanced from the intake manifold to the combustion chamber through the intake valve. Accordingly, as the lubricating oil is advanced through the intake valve, lubricating oil is deposited on the components of the intake valve, such as the valve member.
There have been instances, during operation of a dual fuel diesel engine which incorporates a lubricating system for the intake valve, where the diesel engine continues to combust natural gas even after failure of the pilot fuel injector. One explanation for the continuing combustion of the natural gas is that the flow of lubricating oil provided by the lubricating system which is ultimately advanced into the combustion chamber functions as an ignition source for the natural gas. In particular, as the lubricating oil is compressed within the combustion chamber, the lubricating oil ignites so as to ignite the natural gas in a manner similar to diesel pilot fuel.
Pilot fuel injectors which are used to inject pilot fuel directly into the combustion chamber are relatively expensive as compared to other fuel injectors which do not inject pilot fuel directly into the combustion chamber. This is true since the former fuel injectors must be specially constructed to withstand the temperature and pressure associated with combustion. Thus, eliminating the need of these specially constructed fuel injectors is desirable.
What is needed therefore is a dual fuel diesel engine having a single fuel injector that injects lubricating fuel oil which (i) functions to lubricate the intake valve of the combustion chamber, as well as (ii) functions as an ignition source for the natural gas within the combustion chamber.